Since I checked Rust servers should be fine since the brotli crate is not a binding on the C.
Apparently it doesn't contain a binding to the C library, but it does contain some compatibility and shares design decisions with it. In other words, it's not a clean-room implementation from the spec, but rather it's a port. Since this RCE is triggered by a OOB access, it's unlikely to have made it into the crate, but it's good to keep these things in mind.
Nope, run ldd on cargo; it links to libbrotlidec.so.1. Via libcurl.
Aren't you glad cargo connects to the network whenever it feels like it? I just love it when my build tool does that.
There are 753 crates that drag in brotli this way: https://lib.rs/crates/curl/rev
The real killer is the oath crate. Basically every rust project using OAuth is vulnerable. That's 398 projects on crates.io plus who knows how many binaries (a lot of non-library projects don't bother publishing to crates.io).
Another scary one is "a practical HTTP client that is fun" https://lib.rs/crates/isahc used in 317 crates including sequoia. In case you wanted somebody to steal your private keys.